Engine room blast aboard a propane carrier proves tricky for Williams Fire & Hazard Control
For most people, a visit to the Caribbean island of Trinidad would be stimulating enough. Chauncey Naylor of Williams Fire & Hazard Control got excited for another reason – the increasingly rare opportunity to battle a marine fire.
“That’s my favorite type of job,” Naylor said. “It’s the most exciting work that we do. It’s confined space done in total dark. There may be a collapse or all sorts of crazy things.”
Imagine Naylor’s disappointment when he was told that the engine room fire aboard a 700-foot liquid propane carrier had almost immediately gone out.
“There had been one big explosion with lots of heat and flame, but that was it,” he said. “I asked the guy on the phone why he needed us. He said,‘Well, we need you to declare the engine room safe before we can go in.’”
Then, even before the WF&HC team could depart, a second telephone call came through from Trinidad.
“He said, ‘By the way, there’s eight feet of propane gas in the bottom of the engine room.’”
Pretty Large Bomb
Nothing extraordinary preceded the engine room explosion. The carrier was docked at an LPG facility at the time of the blast. Fortunately, almost the entire crew was on deck having just loaded three cargo pressure vessels – two with propane and one with butane. Each tank averages 2,130 cubic meters of liquid at 80 percent volume of liquid.
One person was in the engine room when the blast occurred.
“They were just getting ready to cast lines and there was this big explosion,” Naylor said. “The guy in the engine room made it out, but he was not in great shape.”
How powerful was the blast? Many of the ladders leading down to the engine room sheared off in the explosion. The few that remained were hanging by one or two bolts.
Ordinarily, at least 20 marine bulkhead doors, all substantial with a two-hour fire rating, seal off the engine room. These passageways were open even though, technically, none of the doors failed.
“The blast simply blew the sealed doors and the surrounding door frames right out of the bulkheads,” Naylor said. “That’s probably what saved the carrier. Structurally, I couldn’t tell where the vessel was disturbed at all.”
Of course, the crew abandoned ship as soon as possible. Upon learning about the propane gas in the engine room, Naylor asked the salvage company if the product tanks had been sealed or “blocked in” and if the space between the cargo and the engine room was monitored and secured.
The salvage company said “yes” to both questions. The only other logical link between the propane cargo and engine room was the heat exchanger, a device used to regulate the temperature and physical state of product – gas or liquid – during transfers.
“This exchanger regulates the temperature using sea water,” Naylor said. “It is pumped out of the sea chest, which is an opening to the sea in the bottom of the ship. The water is circulated through the exchanger and returned to the sea.”
Speculation is that one or more tubes used to move gas through the exchanger breached. As the gas warmed and expanded, it forced its way through the pump seals into the engine room. Finding an ignition source, the propane then fueled the violent but brief explosion.
“The explosion rapidly depleted the flammable vapor, putting out the fire,” Naylor said. “But the propane still trapped in the heat exchanger continued to expand and escape. Only now there was no ignition source because the engines were dead.”
An eight-foot-deep layer of dense propane gas soon wafted above the engine room’s lower deck and in the space between the storage tanks.
Working from top deck inside the engine room six stories above the floor, the WF&HC team first lowered gas detectors to determine the exact explosive range involved.
“In the three feet above the eight foot layer of propane, the LEL (lower explosive limit) was 50 percent,” Naylor said. “Above that the LEL dropped to zero because the vapor density of the propane was heavier than air. The smell of the odorized gas wasn’t even reaching the top deck.”
Below eight feet, the propane was thick and too rich to burn. However, in that outside fringe just beyond the visible vapor the gas and oxygen mixture was well within the flammable and potentially explosive range.
All this meant that the emergency responders were “standing on a pretty large bomb,” Naylor said.
Tag Line Trauma
Enough oxygen to support combustion does not necessarily mean enough to support human life. Available oxygen below the carrier’s top deck plunged to only four percent. With anything less than 16 percent fatal, the WF&HC crew making entry would have to wear breathing apparatus.
“We were on supplied air plus an escape pack,” Naylor said. “Working with supplied air tag lines can be a pain in the butt. With two or three people using them, they can get crossed up real easy.”
Naylor decided to play guinea pig and be the first to visit the engine room.
“I wanted to see if I could reach the target with the tag line I had available before bringing in the others,” Naylor said. “I got all the way to the bottom step of the ladder to the engine room and ran out of line.”
Naylor returned topside and ordered another 50 feet of tag line. Then he tried it again.
“I got to the last step on the ladder and still had slack,” he said. “I took eight more steps and hear ‘pop’ and a loud hiss.”
The tag line had ruptured. Naylor had no outside air.
“This isn’t like a house fire where I can get one breath out of my coat and run out the front door,” he said. “The atmosphere was 99 percent bad gas.”
Using his escape pack, Naylor made it back to safety on the top deck.
“Everybody was freaking out,” he said. “I said, ‘Okay, it’s alright, that’s why we have escape packs,’” he said. “It was a real good moment to have an extra safety meeting, though.”
Open Air Plan
After conferring with various chemists, the WF&HC crew decided to dilute and ultimately inert the atmosphere below deck by pumping carbon dioxide into the carrier.
“I had never realized that carbon dioxide is actually soluble in propane,” Naylor said. “CO2 seemed to be the best choice due to its vapor density, just shy of propane at 1.5.”
Even if conventional ventilation had been possible below the waterline, it would not have been enough to remove the propane, he said. It would only have exchanged the lighter atmosphere above the vapor, leaving the dense propane undisturbed.
“Of course opening a window underwater was not an option,” Naylor said.
The first step would be to reseal the thoroughly ventilated engine room. For this, WF&HC turned to a local contractor well suited to the task.
“They had fire resistant plywood on hand,” Naylor said. “I don’t think I could find fire resistant plywood anywhere in southeast Texas. It was UL listed ¾-inch fire resistant plywood. They also had fire resistant caulking and tape.”
Using nothing but a flashlight and a measuring tape, the contractor measured each opening. Nearly a mile from the scene, workers used battery powered tools to carefully tailor the plywood to each opening.
“Because of the tremendous stress from the explosion, none of the measurements were really absolute,” Naylor said.
When the contractor finished, Naylor said the sealed openings looked “as if the plywood had grown to fit that hole perfectly.” The worst part was telling him to remove one of the sealed openings to give WF&HC access to the engine room, Naylor said.
“We cut open one man-way at the top of the engine room,” he said. “We also had access for our 10-inch tubing exhust duct and fire-water lines.”
Monitoring tubing, arranged in 12-inch increments above the engine room floor, allowed responders to take samples at varying heights from outside without resorting to SCBA. The water lines powered closed circuit ventilation fans specifically designed to operate in potentially hazardous environments
WF&HC proceeded to pump two truck loads of carbon dioxide into the carrier, using an evaporator to warm and expand the liquid CO2. Delivering the gas required two 500-foot lays of 1½–inch gas hose terminated at a pair of two-inch diameter gas diffusers fabricated on site by WFHC Personnel.
Responders placed the assemblies inside the engine room and tied it off on a mezzanine deck at the carrier’s 02 level. Introducing the CO2 took nearly 24 hours.
“We figured we had filled the available space nearly six times over by volume,” Naylor said. “One chemist we trust estimated the saturation rate at about 800 to one. We didn’t have enough space for 800 times the eight feet of gas but anything is better than nothing.”
Time had come for another look inside the engine room. The WF&HC crew donned SCBA and made their way inside.
“ Propane and CO2 are crystal clear,” Naylor said. “It was the first engine room I can remember where you turned your flashlight on after an explosion and could see everything. It was like being underwater in the Arctic where the water is so clear divers develop a fear of falling.”
Nothing in the engine room had been untouched by the explosion, he said.
“Everything that wasn’t steel was melted and hanging down,” Naylor said. “All the wiring was burned and the covers on the engines had been destroyed.”
In particular, the extent of the damage came as a shock to the carrier’s chief engineer, he said.
“He was out on the top deck at the time,” Naylor said. “He just knew that as soon as we got that engine room cleared he was going to turn the ignition and drive his boat home.”
Out to Sea
Next, the saturated CO2 had to be removed. Tugs towed the carrier 10 miles offshore for this phase at the insistence of local authorities. Responders again sealed the engine room and began filling the carrier’s bilge with water to force any residual propane out of the open areas between the tanks.
“The plan was to fill the voids with water and press the gas upward so we could mechanically vacuum it off using closed circuit water powered ventilation fans,” Naylor said. “However, that could bring the space back into the flammable range.”
To counter any introduction of oxygen during ventilation, the WF&HC crew employed a diesel burning inert gas generator. The generator produces inert gas, mostly carbon monoxide.
To vacuum out the bad gas, the fans drew the atmosphere into a suction pipe that routed it off the carrier.
“Each fan moves about 2,000 cubic feet per minute with 200 pounds per square inch of fire water driving the closed circuit unit,” Naylor said. “We wanted to move this atmosphere out at least twice before we did anything else. We ended up running the inert gas generator about 24 hours to give us a somewhat positive pressure atmosphere.”
Responders made sure to run the generator a sufficient period first before starting the ventilation fans.
“When we started to pull air out, something was going to replace it,” Naylor said. “We didn’t want any chance of sucking oxygen into that environment.
When it came time to activate the fans, Naylor did not feel anything pushing through the exhaust hose.
“I was afraid we were dumping more water into the bilge area,” Naylor said. “We had already put enough water in the bilge to accomplish what we wanted. I didn’t want to upset the stability of the situation.”
Naylor and Eric LaVergne reopened the carrier’s interior and stepped into a big surprise.
“It had gone from being super clear and cool to being as hot as if we had a fire again,” Naylor said. “I knew that wasn’t possible.”
The responders soon deduced what was wrong. The heat from the original flash fire and explosion had been absorbed into the carrier’s steel. Now, with all ventilation closed and no air movement, the steel began releasing that heat.
“Plus, the visibility was zero,” Naylor said. “All that nasty exhaust was hovering in the air.”
Naylor and LaVergne discovered that one hose had been cross connected and was pouring into the galley on the main deck.
“We threw it out the window and went to work,” Naylor said.
With the fans now activated, atmosphere exiting the exhaust system was doused with water using a fog nozzle stream from a 2,000 gpm Daspit tool mounted on the side railing of the carrier in a final effort to dissipate the gas.
After running the fans for 20 hours, an air sample showed that the LEL had dropped to an acceptable level. Within another five hours, responders opened up the carrier’s interior to fresh air.
Naylor, director of emergency response training and education operations for WF&HC, began his career in fire fighting with the Port Everglades (FL) Public Safety Fire Department. Ten years there qualified him to join WF&HC in 1996.
Marine fire fighting may be his first love, but the challenging events that Naylor specializes in are becoming few and far between.
“We’ve had six in the last 15 years that were notable,” he said.
Williams F&HC is not a marine company, he said.
“It’s not what we base our business on,” Naylor said. “But we are always available for marine response. If there is a seventh fire added to the challenging list, we’ll probably get the call.”